XRT79L71
PRELIMINARY
121
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Test Signal
Idle Signal
CL Path Identification
ITU Path Identification
The ITU Path Identification type of PMDL Message consists of an 82-byte information payload. All of the
remaining standard types of PMDL/LAPD Messages contain 76 byte information payloads. To transmit an 82
byte message (e.g., the ITU Path Identification type of LAPD Message), then the user should set Bit 1
(Transmit LAPD Message Length), within the Transmit DS3 LAPD Configuration Register to "1". For all of the
remaining types of LAPD Messages which are 76 bytes in length, the user should set Bit 1 (Transmit LAPD
Message Length) to "0". This operation is depicted below.
NOTE: This setting will configure the Transmit LAPD Controller to handle LAPD/PMDL messages that contain 76-byte sized
Information Payloads.
To transmit an ITU Path Identification type of PMDL Message, then the user needs to write the value "1" into
the Transmit LAPD Message Length bit-field, as depicted below.
NOTE: This setting will configure the Transmit LAPD Controller to handle 82-byte sized PMDL Messages.
STEP 5 - Load the Transmit LAPD Message Buffer
The next step is to load in the contents of the outbound PMDL/LAPD Message into the Transmit LAPD
Message Buffer. Whenever the user wishes to load in the contents of the outbound PMDL/LAPD Message into
the Transmit LAPD Message buffer, then the user MUST employ the Indirect Addressing scheme that will be
presented below.
In order to begin the process of loading in the contents of the outbound PMDL Message, the user must be
aware of the following important Address Locations, within the XRT79L71 Address space.
1.
The LAPD Message Buffer - Indirect Address Register - Address = 0x11C0
2.
The LAPD Message Buffer - Indirect Data Register - Address = 0x11C1
By performing READ or WRITE operations to these two registers, the user can actually obtain READ/WRITE
access to both the Transmit LAPD Message Buffer and the Receive LAPD Message Buffer. This section will
Transmit DS3 LAPD Configuration Register (Address = 0x1133)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LAPD Any
Unused
Auto Retransmit
Unused
Transmit LAPD
Message
Length
Transmit LAPD
Enable
R/W
RO
R/O
R/W
R/O
R/W
0
X
0
1
Transmit DS3 LAPD Configuration Register (Address = 0x1133)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LAPD Any
Unused
Auto Retransmit
Unused
Transmit LAPD
Message
Length
Transmit LAPD
Enable
R/W
RO
R/O
R/W
R/O
R/W
0
X
0
1